1. Field of the Invention
The present invention relates to an image input apparatus configured to form a composite image based on a photoelectric conversion signal and a saturation signal. Furthermore, the present invention relates to a control method for the image input apparatus.
2. Description of the Related Art
Digital cameras or other image input apparatuses use a solid-state image sensor, such as a CMOS (complementary metal-oxide semiconductor), having a narrow dynamic range compared to conventional silver-halide photography. To compensate for this drawback, Japanese Patent Application Laid-Open No. 2003-18471 discusses a method for enlarging the dynamic range based on photoelectric saturation charge flowing into a reading section of an imaging element obtainable when a light-sensitive element receives incident light exceeding its capacity.
According to a conventional method for enlarging the dynamic range, a saturated light quantity signal representing photoelectric charge flowing into the reading section and a light-sensitive element signal stored in the light-sensitive element, are independently read out and simply added to obtain an image having an enlarged dynamic range.
However, a reading section of an ordinary solid-state image sensor is not essentially configured to store the photoelectric charge overflowing from a light-sensitive element. If a signal obtained from the reading section is combined with a light-sensitive element signal without any correction, the resultant composite image will contain a significant amount of noise component and its gradation will be unnatural.